1. Technical Field
The present invention relates to a sheath for providing vascular access. More particularly, the invention relates to a thin-walled, flexible, kink resistant introducer sheath, and a method of manufacturing a sheath.
2. Background Information
Introducer sheaths or catheters are widely used as conduits to provide percutaneous access to the vascular system. For optimal use, it is desired that such sheaths have as thin-wall construction as possible, in view of the nature of the sheath. In addition, it is desired that such sheaths be flexible and kink resistant, so that they can traverse the narrow confines of the vascular system. Further, it is desired that such sheaths be amenable to manufacture by cost effective means.
Many existing sheaths fall short of one or more of these objectives. For example, in order to improve the level of kink resistance, some manufacturers have deemed it necessary to provide a sheath having a relatively thick sheath wall. Increasing the thickness of the wall of a sheath may improve the level of kink resistance somewhat when compared to a thin-walled sheath, however the level of kink resistance may still be insufficient for some intended uses. In addition, increasing the thickness of the sheath wall is inherently undesirable, because in order to accommodate the increased size of the sheath, a larger entry opening must be made in the body vessel than would otherwise be required. On the other hand, in order to reduce the size of the entry opening required, some manufacturers provide a sheath having a relatively thin wall. However, a thin-walled sheath may adversely affect the kink resistance and the pushability of the sheath. Thus, there is generally a trade-off that must be made during construction of a sheath, so that the various desirable properties may be optimized to the greatest extent possible, consistent with the intended use of the sheath.
Sheaths used in certain medical procedures in which a fluid is to be introduced and/or removed from the vasculature of a patient, such as hemofiltration and dialysis procedures, are particularly prone to kinking. Such sheaths must remain positioned in a patient's body for an extended period of time, and as a result, are prone to being bent or pinched off. A kinked sheath is unusable, and cannot be straightened while positioned in the body of a patient. Consequently, the sheath must be removed, leaving an enlarged, bleeding opening which typically cannot be reused. Vascular access must then be re-attempted at an alternative site, and the procedure is restarted. Restarting the procedure causes a time delay, which is inconvenient, and at times may be life threatening. In addition, in some cases, an acceptable alternative site may not be readily available for introducing another sheath.
Another problem with existing introducer sheaths is that the sheath may kink when a physician attempts to insert an interventional device, such as a catheter or a stent, through the sheath during an emergency procedure. Small diameter introducer sheaths are particularly prone to being bent and kinked under the time constraints that arise during an emergency situation. If kinking occurs, the sheath becomes unusable and a new sheath must be introduced at the same or another access site.
It is desired to provide a thin-walled introducer sheath that has sufficient stiffness and kink resistance to permit it to be introduced into the vascular system to perform an interventional procedure, and that is sufficiently flexible to permit it to be directed to appropriate sites within the vasculature of a patient. It is further desired to provide a cost efficient method of making a flexible, kink resistant sheath.